1. Field of the Invention
The present invention relates to a surface-tracking measuring machine. More specifically, the present invention relates to a surface-tracking measuring machine for measuring a surface roughness and a profile of a workpiece by relatively moving both a tracer and the workpiece while abutting the tracer onto a surface of the workpiece.
2. Description of Related Art
A tracer-type surface roughness measuring machine is known as a measuring machine for measuring a surface roughness of the workpiece.
The tracer-type surface roughness measuring machine includes a main body, a probe swingably supported by the main body and having a tracer at an end thereof, a biasing device for biasing the tracer of the probe to touch the surface of the workpiece, a moving device for moving the probe in a direction approximately orthogonal with the tracer, and a displacement sensor for detecting a swing displacement amount of the probe.
In measuring the surface roughness of the workpiece, the probe is moved along the surface of the workpiece by the moving device while the tracer of the probe is in contact with the surface of the workpiece, and the swing displacement amount is detected by the displacement sensor. The surface roughness of the workpiece can be obtained by the swing displacement amount and the amount of movement of the probe.
Generally speaking, the following performance is required for the tracer-type surface roughness measuring machine.
First, a low measuring force for preventing scratch marks on the surface of the workpiece.
Second, good tracking ability for the tracer to accurately trace the sectional curve.
Third, high-resolution for detecting minute concave and convex features on the surface of the workpiece.
Conventionally, a spring is used as the biasing device for biasing the tracer of the probe to the surface of the workpiece. However, in order to lower the measuring force in accordance with the above first condition, the magnitude of the biasing device is limited.
Accordingly, in order to obtain the necessary tracking ability, the size and weight of the probe has to be reduced as much as possible. Further, the displacement sensor for detecting the swing displacement amount of the probe has to be selected from sensors, such as a differential transformer, a strain gauge, a capacitive sensor, and an optical lever, which applies less load for actuating the probe.
Ordinarily, the measurement range of the tracer-type surface roughness measuring machine is around 1 mm. According to a conventional arrangement, when the measurement range is to be solely widened, some kind of deterioration in performance such as deterioration of the resolution of the displacement sensor, deterioration of responsivity on account of increase of movable portion weight, and increased fluctuation of measuring force is inevitable, which results in difficulty in enlarging the measurement range.
Accordingly, the conventional tracer-type surface roughness measuring machine can not also be used as a profile measuring machine for measuring the profile of the workpiece. In other words, the surface roughness of the workpiece has to be measured by the surface roughness measuring machine and the profile of the workpiece has to be measured separately by the profile measuring machine.